The present invention relates generally to roof structures including moisture vapor vents and more particularly to a roof structure in combination with a one-way moisture vapor vent.
A typical roof structure to which the present invention relates includes a roof deck, roof insulation disposed over the deck and the built-up roof disposed over the insulation. It has long been recognized that this type of structure includes residual moisture within, particularly at the time it is assembled together. This is particularly true where the deck is constructed of wood and the insulation is standard perlite-type board. Even a "cured" wooden deck includes a certain amount of residual moisture which escapes only with time and the application of ambient heat. This is equally true of standard perlite board which typically includes as much as 7 percent moisture at the time it is manufactured. There is also a tendency for moisture to be captured between the various layers of the roof structure, i.e., between the roof deck and insulation and between the insulation and built-up roof. This results generally from the fact that these three components are assembled together in the field, quite often over a relatively long period of time. Hence, they are exposed to ambient moisture, even rain, which not only penetrates into the components but also collects therebetween.
The roof structure once assembled is subjected to the ambient surroundings and, as is well known, can become very hot, particularly where the roof structure is located in warm to hot climates. As a result, the moisture within the structure has a tendency to heat up and convert to vapor in a pressurized state greater than that of the ambient surroundings. It has long been recognized that this pressurized vapor is one main cause of blistering in the built-up roof and that this blistering problem can be reduced by providing positive venting points for the passage of the moisture vapor to the ambient surrounds. Accordingly, most roof structures of the type described above include conventional open ended vents located at various points along the structure.
These vents, i.e., open ended tubes, just described are prefectly satisfactory for venting moisture from within the roof structure, i.e., within the roof deck, insulation and built-up roof and therebetween to the ambient surroundings. However, Applicant has discovered that the venting of this moisture to the ambient surroundings results in voids within the roof structure and specifically, that these voids produce sufficient back pressure to "draw" moisture from the ambient surroundings back into the roof structure through the tubular vents. Generally, Applicant has found that while moisture vapor which builds up within the roof structure during the heat of the day passes out through the vents, during the night, under much cooler conditions, moisture within the ambient surroundings is drawn back into the structure through the vents. It is not necessarily true that this entire intake of moisture during the cooler period is completely vented back into the ambient surroundings the next day. Rather, it is quite possible that some of this moisture never escapes but rather aids in the blistering problem discussed above.
As will be seen hereinafter, the present invention is directed to minimizing if not eliminating this drawback in standard venting practice by combining a one-way vent with a roof structure of the type described above. In this regard, Applicant has found that the pressure buildup within the roof structure resulting from the moisture vapor therein is sufficiently high before actual passage of the moisture and that the pressure within the roof structure after passage of the moisture vapor is sufficiently low to operate a one-way vent, i.e., to allow escape of the moisture vapor to the ambient surroundings but to prevent moisture vapor from being drawn back into the roof structure through the vent.